No. The only benefits you get from multiclassing in 4e are the ones listed in the multiclass feat description. In other words, when you multiclass into Paladin, you get skill training in one Paladin class skill, Divine Challenge once per encounter, and you can use Paladin implements. That's it. No weapon proficiencies, no armor proficiencies, no attack powers, no Lay on Hands, no increased Healing Surges, no extra HPs on level up, nothing beyond what's stated in the feat description. It's a LOT simpler than in earlier editions.